The pressure generated by fans in ductwork is typically very small. An accurate measurement of static presure is critical to proper fan selection however. Static pressure in fan systems is typically less than 2" SP, or 0.072 Psi.
The amount of static pressure that the fan must overcome depends on the air velocity in the ductwork, the number of duct turns (and other resistive elements), and the duct length. For properly designed systems with sufficient make-up air, the guidelines in the table below can be used for estimating static pressure.
*Starred items represent required fields.
Static Pressure Guidelines
Non-Ducted 0.05" to 0.20"
Ducted 0.20" to 0.40" per 100 feet of duct (assuming duct air velocity falls within 1,000 to 1,800 feet per minute)
Important: Static pressure requirements are significantly affected by the amount of make-up air supplied to an area. Insufficient make-up air will increase static pressure and reduce the amount of air that will be exhausted. Remember, for each cubic foot of air exhausted, one cubic foot of air must be supplied.